The simplest spectroscope splits incident visible light into spectral lines that can be observed by the human eye. In more complicated analysis, for example spectrochemical analysis, the substance under investigation is heated, so that it emits radiation. Each component of the substance emits a characteristic radiation, and this can be used as a means of identification. The radiation is passed through a diffraction grating or a prism to separate it into its constituent wavelengths. Detectors are then used to observe or record details of the spectrum, and instrument can be used to measure the wavelengths and intensities of spectral lines. A permanent record of the results (a spectrograph) may be made to allow more detailed analysis. Comparison of the spectrum with the spectra of known, pure, substances allows the components to be identified and, with quantitative analysis, their relative proportions determined. This offers an extremely sensitive method of analysis of chemical substances, and automated spectroscopic procedures are now used routinely in laboratories.
Most laboratory apparatus are currently used for the measurement of the concentration of a material in a solution are relatively complex in nature. Their degree of complexity is at least partially a cause for several disadvantages firstly they are relatively expensive. Secondly they are often relatively delicate as they use prisms and dispersion gratings and are generally unsuitable for use in the field or in normal manufacturing and processing environments. And thirdly they are generally specific in purpose and often cannot be readily adapted for other applications.
The term ‘material’ shall be used in its broadest sense and shall not be restricted to solid matter but also to liquids or gases. In addition the term ‘solution’ shall also be taken to include the gaseous phase.
International patent application number WO96/31764 discloses a method and apparatus for the quantitative determination of particles in fluid. This apparatus comprises one or more light emitters, and one or more light detectors sensitive to the output of the emitters. Data is gathered from a plurality of signal paths between the emitter and detector. This data is subsequently evaluated by comparison with known data for different fluid particles in a fluid sample.
U.S. Pat. No. 4,158,505 describes a spectrophotometer consisting of a wideband light source, paths provided for the sample and reference lights, a chopper wheel allowing the sample and reference light to be interspersed with dark period, and be alternately incident on a dispersion grating and thus transmitted onto a linear array of photodiodes.
U.S. Pat. No. 3,955,082 describes a single photodetector for measuring a variety of wavelengths. The single photodetector is constructed from a plurality of detector sections each having a variable bandwidth and controlled by varying the reverse bias voltage.
U.S. Pat. No. 5,357,343 describes a spectrophotometer consisting of a single emitter detector and rotating chopper. The rotary chopper contains filters to select wavelengths to be incident on the detector at anyone time. All the inventions described in each specification possess many of the general disadvantages described previously.